This invention is directed to range determining systems and, more particularly, to passive radar range determining systems.
In certain military environments, it is desirable to be able to passively, readily and rapidly, determine the range from an object, such as an aircraft, to a radiating radar antenna. It may be desirable, for example, to know this information in order to destroy the antenna. While this information can be obtained utilizing standard triangulation techniques wherein an aircraft flies a base line between two different locations in order to obtain direction information, such a procedure is time consuming and, therefore, undesirable.
In order to overcome the above-noted problem, it has been proposed to utilize two receiving antennas mounted on a single aircraft and determine the time difference (time shift) between receipt of signals by the two antennas in order to determine the range between the aircraft and the transmitting antenna. However, prior to the present invention no satisfactory apparatus for determining the very small time difference involved has been proposed. More specifically, the major difficulty with using this technique relates to the fact that the spacing between the two antennas, and the frequency of the received video pulse train, is such that the signals received by the two antennas overlap to the degree that they are almost superimposed. The resultant very small time shift between the two signals is difficult to measure using classical circuits.
Therefore, it is an object of this invention to provide a processor suitable for determining the time shift between overlapping nearly identical signals.
It is a further object of this invention to provide a processor suitable for use in a passive radar ranging system for determining the time shift between the envelopes of two overlapping video pulse trains.
It is a further object of this invention to provide a processor suitable for measuring the extremely small time shift between pulse train envelopes which are of narrow but non-zero bandwidths, and overlap in time.